Single-site catalysts are known. They can be divided into metallocenes and non-metallocenes. Metallocene single-site catalysts are transition metal compounds that contain cyclopentadienyl (Cp) or Cp derivative ligands. Non-metallocene single-site catalysts contain ligands other than Cp but have similar catalytic characteristics to the metallocenes. The non-metallocene single-site catalysts often contain heteroatomic ligands, e.g., boraary, pyrrolyl, azaborolinyl, indenoindolyl and quinolinyl.
Aluminoxane compounds are activators for single-site catalysts. There are many ways to make aluminoxane compounds. For instance, aluminoxanes can be produced by contacting a trialkylaluminum compound with water. See U.S. Pat. No. 5,041,585. Commonly used aluminoxane is methyl aluminoxane (MAO) or its derivatives.
Methods for modifying aluminoxanes are known. For instance, U.S. Pat. No. 6,340,771 teaches modifying MAO with sugar to make “sweet” MAO. Also, U.S. Pat. No. 5,543,377 teaches modifying aluminoxane compounds with ketoalcohols and β-diketones.
Single-site catalysts produce polyolefin having narrow molecular weight distribution. The uniformity of molecular weight distribution of single-site polyolefin, although improving tensile strength and other physical properties of polymer products, makes the thermal processing difficult. Many methods have been developed to improve processability of single-site polyolefin. U.S. Pat. No. 6,127,484, for example, teaches a multiple-zone, multiple-catalyst process for making polyethylene. The polymer produced has a broad molecular weight distribution and improved processability.
New methods for modifying aluminoxane compounds are needed. Ideally, the method would be inexpensive and easy to practice. Particularly, the modified aluminoxane would increase molecular weight distribution and improve the processability of single-site polyolefin.